Many electronic devices make use of an internal or external power supply unit for the provision of electrical operating energy from a mains voltage. For example, computer screens, such as LCD monitors, printers or scanners are usually connected to a mains voltage for operation. Often such electronic devices comprise at least one energy saving state, in which most of the functionality of the device is disabled. In such energy saving states, the electric power consumption of the electronic device is greatly reduced. For example, an LCD monitor having a typical power consumption of 40 W when in operation, may only consume power of 2 to 4 W in a so-called stand-by mode by deactivating a background illumination unit and/or a scaling unit.
However, even in stand-by or other energy saving states, the electronic device still needs to be supplied with at least some electrical energy. This is partly so because the electronic device needs to monitor input elements or connections in order to determine whether it is time to return to a full operating mode. For example, a printer may monitor a network port to observe if there is any new print job available. Because power supply units typically have a lower efficiency, if only a fraction of the nominal output power is consumed, the total loss of energy in stand-by mode may be substantial.